Grinding mills use grinding discs on a rotating shaft to agitate a grinding media load within a housing. The grinding discs are vertically stacked within the housing and are typically separated by spacers placed between each grinding disc (i.e.—a disc stack). As coarse slurry enters one end of the grinding mill and moves to an opposite end, it is sheared and pulverized between the grinding media and the rotating grinding discs. At the opposite end of the grinding mill, finer slurry exits the housing. Accordingly, particle sizes within the slurry are reduced.
One example of such a grinding mill is the FLSmidth® VXPmill™ vertical regrind mill (formally known as the Knelson-Deswik VGM-series mill). The mill has a series of grinding discs (i.e.—a disc stack) which rotate within a barrel-shaped vertical housing filled with grinding media to pulverize particles in coarse feed slurry.
Grinding discs must typically be replaced every three to eight months (depending on the tip speed of the grinding mill) because of excessive wear due to the impact of the grinding media against the grinding discs within the housing. Depending on the volume and mass of the grinding media used within a typical grinding mill, the first third of the total number of grinding discs which are located closest to the slurry feed inlet typically exhibit the greatest amount of wear and are required to be replaced more frequently. In many cases, this first third comprises approximately four grinding discs.
To perform maintenance on grinding discs (for example to remove or replace them) technicians open and drop the bottom flange of the housing base, install bar supports (for example Z-shaped bar supports) on each individual grinding disc within the housing, remove the disc cover from the hub of the bottom-most grinding disc, remove the screws and/or bolts securing each individual grinding disc (typically using a torque tool) and thereafter use a chain hoist to lower each individual grinding disc out of the housing to the ground level. To reach the second or third vertically stacked grinding discs technicians may be required to climb or reach into the housing in order to remove the screws and/or bolts.
The maintenance process using prior art systems as described above is time consuming, burdensome and dangerous and can result in injuries to technicians, superfluous operational downtime, increased labor costs and reduced throughput due to less frequent replacement of grinding discs due to the foregoing disadvantages. For example, it takes a significant amount of time to install Z-shaped bar supports under each of the individual grinding discs within the housing. Each of the Z-shaped supports are required to be attached to the housing with axial screws and/or bolts and rotated into place between each grinding disc. Installing the Z-shaped supports is also burdensome and unsafe. Technicians are required to work within the confines of the housing and are subjected to large, heavy suspended loads. Technician error in installing the individual Z-shaped bar supports result in significant down time, increased labor costs and injuries. Additionally, technicians spend more time removing the screws and/or bolts securing each individual grinding disc because their mobility within the housing is limited. This results in additional downtime and increased labor costs.
We have determined that a new type of maintenance apparatus is needed in order to increase safety and to reduce the costs and time associated with the maintenance of grinding discs. According to some embodiments, advantages which may be realized through the practice of our invention may include one or more of the following: providing a safer environment for technicians to perform maintenance on grinding discs, reducing maintenance costs associated with the removal and replacement of grinding discs and reducing the time-consuming process for removing such discs which may result in increased throughput, without limitation.